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Computer Networks I Week 1,2 Computer Networks A computer network consists of two or more computing devices that are connected in order to share the components of the network (its resources) and the information A network consists of two or more computers that are linked in order to share resources (such as printers), exchange files, or allow communications.Commonly used in the following situations: o Wireless installations - attach antennas to wireless devices o Cable internet installations - customer premises wiring Ethernet Straight-through and Crossover UTP Cables Connections of a Router for Ethernet ?Straight through used to connect: o Switch-to-Router, Switch?to-PC, Router-to-Server, Hub-to-PC, Hub-to-Server ?Cross-over used to connect: o Switch-to-Switch, PC-to?PC, Switch-to-Hub, Hub?to-Hub, Router-to-Router Cisco Network Academy, https://www.netacad.com/courses/ Fiber-Optic Cabling Properties of Fiber-Optic Cabling o Not as common as UTP because of the expense involved o Ideal for some networking scenarios o Transmits data over longer distances at higher bandwidth than any other networking media o The fiber-optic cable acts as a wave guide to transmit light between the two ends with minimal signal loss Fiber-Optic Cabling Fiber versus Copper Implementation Issues UTP Cabling Fiber-Optic Cabling Bandwidth supported 10 Mb/s - 10 Gb/s 10 Mb/s - 100 Gb/s Distance Relatively short (1 - 100 meters) Relatively long ( 1 - 100,000 meters) Immunity to electrical hazards Low High (Completely immune) Media and connector costs Lowest Highest Installation skills required Lowest Highest Safety precautions Lowest Highest Wireless Media Properties of Wireless Media It carries electromagnetic signals representing binary digits using radio or microwave frequencies.Classful Addressing Classification based on the leading bits of the first octet Cls First Octet (Decimal) First Octet (Binary) Default Subnet Mask Max Hosts per Network Typical Use CIDR / Slash Dotted Decimal A 1 - 126 0 xxxxxxx 1b fixed 7b variable /8 255.0.0.0 16,777,214 128 networks Large -- ISPs, governments, enterprises B 128 - 191 10 xxxxxx 2b fixed 6b variable /16 255.255.0.0 65,534 16,384 networks Medium -- universities, large organisations C 192 - 223 110 xxxxx 3b fixed 5b variable /24 255.255.255.0 254 2,097,152 networks Small -- homes, small offices D 224 - 239 1110 xxxx 4b fixed 4b variable -- -- (N/A) Multicast only Reserved -- Multicast traffic Fixed bits -- identify the class Variable bits -- network / host portion Source: RFC 791 -- IANA Classful Network Addressing o Sub-netting is the process of dividing a Class A, B or C network into subnets.Unit of Bandwidth Abbreviation Equivalence Bits per second bps 1 bps = fundamental unit of bandwidth Kilobits per second Kbps 1 Kbps = 1,000 bps = 103 bps Megabits per second Mbps 1 Mbps = 1,000,000 bps = 106 bps Gigabits per second Gbps 1 Gbps - 1,000,000,000 bps = 109 bps Terabits per second Tbps 1 Tbps = 1,000,000,000,000 bps = 1012 bps Physical Layer Characteristics Bandwidth Terminology Latency o Amount of time, including delays, for data to travel from one given point to another Throughput o The measure of the transfer of bits across the media over a given period of time Goodput o The measure of usable data transferred over a given period of time o Goodput = Throughput - traffic overhead o Traffic Overhead: This is the extra data added to manage the transfer, such as packet headers, error-checking bits, or control information Copper Cabling Characteristics of Copper Cabling Copper cabling is the most common type of cabling used in networks today.UDP examples: live video, VoIP, online gaming TCP Features o Establishing a Session o Connection-oriented protocol o Ensures the application is ready to receive the data o Reliable Delivery o Ensuring that each segment that the source sends arrives at the destination o Same-Order Delivery o Numbering & Sequencing the segments guarantees reassembly into the proper order o Flow Control o Regulate the amount of data the source transmits TCP Header o TCP is a stateful protocol which means it keeps track of the state of the communication session.Whenever another host sent traffic to 10.10.10.10, the network wouldn't know which one to send it to. o We could have host 10.10.10.10 on one subnet and host 10.10.20.10 on another subnet www.su.edu.om The Network Address (Network ID) o 192.168.10.15 / 255.255.255.0 o All 0's in the host portion designates the network address and is not allowed to be allocated to a host o In our example the network address is 192.168.10.0 From Salih ALPEREN to Every www.su.edu.om The Broadcast Address o 192.168.10.15 / 255.255.255.0 o All 1's designates the directed broadcast address for the subnet o Traffic with this destination address will be sent to all hosts in the subnet o In our example the broadcast address is 192.168.10.255 www.su.edu.om Host Addresses o That leaves 192.168.10.1 to 192.168.10.254 available to be allocated to hosts www.su.edu.om Subnet Mask in Slash Notation o 192.168.10.15 / 255.255.255.0 o Because the subnet mask always begins with contiguous '1's, it will be 1 to 32 bits long counting from left to right o This allows us to write the subnet mask in slash notation which is more convenient than dotted decimal for network diagrams or in conversation www.su.edu.om Subnet Mask in Slash Notation o Our example can be written as either 192.168.10.15 255.255.255.0 or 192.168.10.15/24 o The network address is 192.168.10.0/24 o This example can be written as either 10.10.10.15 255.0.0.0 or 10.10.10.15/8 o The network address is 10.0.0.0/8 www.su.edu.om Subnet Size o The bigger the host portion of the network, the more hosts we can have o If the subnet mask is /8, we have 24 bits available to allocate to hosts o If the subnet mask is /24, we only have 8 bits available to allocate to hosts Logical AND ?Cisco Confidential Peer-to-Peer Networks (Cont.) Advantages of P2P networking: o Easy to set up o Less complex o Lower cost because network devices and dedicated servers may not be required o Can be used for simple tasks such as transferring files and sharing printers Disadvantages of P2P networking: o No centralized administration o Not as secure o Not scalable o All devices may act as both clients and servers which can slow their performance 9 Network Types o Two most common types of networks: o Local Area Network (LAN) - spans a small geographic area owned or operated by an individual or IT department.Borrowing Host Bits o Let's say we've been allocated Class C 200.15.10.0/24 o To subnet the network into smaller subnets, we need to 'borrow' host bits and add them to the network portion of the address o The network address line always moves to the right when we subnet o The further to the right we go, the more subnets we'll have of that size but less hosts Calculating the Number of Networks o To calculate the number of available subnets, the formula is 2 subnet-bits o If a Class C network uses a /28 subnet mask then we've borrowed 4 bits from the default of /24 o 2 4 = 16 available subnets o If a Class B network uses a /28 subnet mask then we've borrowed 12 bits from the default of /16 o 2 12 = 4096 available subnets o Hosts on different subnets need to go via a router if they want to communicate with each other Calculating the Number of Hosts o To calculate the number of available hosts, the formula is 2 host-bits - 2, o We subtract 2 because the network address and broadcast address cannot be assigned to hosts o If a Class C network uses a /28 subnet mask then we have 4 bits left for hosts 2 4 -2=14 o If a Class B network uses a /28 subnet mask then we have 4 bits left for hosts 2 4 -2=14 Class C /31 Subnet o Let's say we've been allocated Class C 200.15.10.0/24 o If we move the line all the way to the right we're now using /31 (or 255.255.255.254) o This leaves one bit for the host address, with a possible value of 0 or 1 o It borrows 7 bits for the network address o This gives us 128 subnets (2 7 ) which accommodate 2 hosts each Class C /31 Subnet o Let's say we've been allocated Class C 200.15.10.0/24 o We subnet using /31.o Otherwise it's in a different subnet and traffic must be sent via a router 192.168.10.15 / 255.255.255.0 www.su.edu.om Valid Subnet Masks o 192.168.10.15 / 255.255.255.0 o The subnet mask always begins with contiguous '1's o For example, 11111111.11110000.00000000.00000000 is a legal subnet mask o 11101101.11110000.11100000.00001111 is not www.su.edu.om Host Portion o 192.168.10.15 / 255.255.255.0 o The host portion of the addressis available to be allocated to the different hosts on the subnet (eg PCs, Servers, Printers, Router Interfaces and Switch Management Addresses) o With two exceptions (coming up after the next slide)...CIDR Classless Inter-Domain Routing o A problem with classful addresses was that if a company had more than 254 hosts they would need to be assigned a Class B network o They would have much less than the 65,534 hosts allocated, so this wasted a huge amount of the global address space o Classless Inter-Domain Routing (CIDR) was introduced in 1993 to alleviate this problem CIDR Classless Inter-Domain Routing o CIDR removed the fixed /8, /16 and /24 requirements for the address classes, and allowed them to be split or 'subnetted' into smaller networks o For example 175.10.10.0/20 o Companies can now be allocated an address range which more closely matches their needs and does not waste addresses Subnetting o Think about it from the point of view of the originally intended IPv4 design again, where all hosts which can communicate on the Internet have a public IP address.www.su.edu.om ARP Address Resolution Protocol www.su.edu.om ARP Address Resolution Protocol www.su.edu.om ARP Address Resolution Protocol www.su.edu.om ARP Address Resolution Protocol www.su.edu.om ARP Address Resolution Protocol www.su.edu.om Routed Traffic o When the sender and receiver are on different IP subnets, the traffic must be forwarded by a router o In the following example, 172.23.4.1/24 wants to send a packet to 192.168.10.1/24 www.su.edu.om Routed Traffic www.su.edu.om Routed Traffic www.su.edu.om Routed Traffic www.su.edu.om Routed Traffic www.su.edu.om Routed Traffic Week 7 www.su.edu.om The Network Layer o The network layer, or OSI Layer 3, provides services to allow end devices to exchange data across networks.Data Link Frame Frame Fields Field Description Frame Start and Stop Identifies beginning and end of frame Addressing Indicatessource and destination nodes Type Identifies encapsulated Layer 3 protocol Control Identifies flow controlservices Data Containsthe frame payload Error Detection Used for determine transmission errors Data Link Frame Layer 2 Addresses o Also referred to as a physical address.Cisco Confidential The MAC Address Table Filtering Frames (Cont.) 35 www.su.edu.om IP to Mac Address resolution o If your network uses the IPv4 communications protocol, you need ARP to map IPv4 addressesto MAC addresses.www.su.edu.om IP Addresses o IPv4 address is expressed as a 32 binary bits and it is divided into Four Octets, each has 8-bits o For example 192.168.10.15 o Each octet is 8 bits long (4x8=32) www.su.edu.om IP Address Octets o Each octet in the IP address has a value ranging from 0 to 255 www.su.edu.om IP Address Octets o 192.168.10.15 =11000000.10101000.00001010.00001111 1 192 168 10 15 2 3 4 www.su.edu.om The Subnet Mask o If the destination is on the same subnet, the host sends traffic directly (through switches).Cisco Confidential Transmission Control Protocol (TCP) o TCP is a connection-oriented transport layer protocol o It provides reliable and ordered data delivery o It uses sequence numbers to track data segments o It uses acknowledgments to confirm received data o It retransmits lost data when necessary o It controls the flow of data between sender and receiver 141 (C) 2020 Cisco and/or its affiliates.o Networks typically use three types of media: o Metallic wires within cables, such as copper o Glass, such as fiber optic cables o Wireless transmission Clients and Servers o Servers are hosts that have software installed which enable them to provide information, like email or web pages, to other hosts on the network.www.su.edu.om The Network Layer o Network layer protocols perform four basic operations : o Addressing end devices - A unique IP address o Encapsulation - The network layer encapsulates the protocol data unit (PDU) from the transport layer into a packet.Copper Cabling Shielded Twisted Pair (STP) o More expensive than UTP o Harder to install than UTP o Terminated with RJ-45 connectors o Interconnects hosts with intermediary network devices Copper Cabling Coaxial Cable There are different types of connectors used with coax cable.o ARP Address Resolution Protocol is used to map the IP address to MAC address www.su.edu.om o The sending device willsearch its ARP table for a destination IPv4 address and a corresponding MAC address: o If the packet's destination IPv4 address is on the same network as the source IPv4 address, the device will search the ARP table for the destination IPv4 address.o The transport layer includes two protocols: o Transmission Control Protocol (TCP) o User Datagram Protocol (UDP) 138 Transport Layer Responsibilities o Tracking Individual Conversation - Tracks each individual conversation flowing between a source and a destination application.To ensure this, all vendors that sell Ethernet devices must register with the IEEE to obtain a unique 6 hexadecimal (i.e., 24-bit or 3-byte) code called the organizationally unique identifier (OUI).www.su.edu.om Subnet 'Masking' o 192.168.10.15 / 255.255.255.0 o The IP address is compared ('masked') with the subnet mask o A '1' in the subnet mask indicates that bit in the IP address is part of the network address o A '0' indicates the bit is part of the host address www.su.edu.om Subnet 'Masking' o 192.168.10.15 / 255.255.255.0 o The IP address is compared ('masked') with the subnet mask o A '1' in the subnet mask indicates that bit in the IP address is part of the network address o A '0' indicates the bit is part of the host address www.su.edu.om The Network Portion o 192.168.10.15 / 255.255.255.0 o In our example, the network address portion is 192.168.10 o The host address portion is .15 www.su.edu.om Local Subnet or Routed Traffic o If the host wants to communicate with another host with an IP address which also begins with 192.168.10.www.su.edu.om Host Address o The host portion of the address specifies the individual host and must be unique on that subnet o Hosts do not have to be numbered sequentially o If the network portion of the address is 10.10.10, you can have a host with IP address 10.10.10.10 and another host with 10.10.10.20 o You can't have two different hosts both with IP address 10.10.10.10.o /26 borrows the first 2 bits in the last octet o 128 + 64 = 192 So the subnet mask is 255.255.255.192 Practice Question Answer o Next let's calculate the address range for this subnet o Write out 198.22.45.173/26 o The network portion of the address is the first 26 bits 198.22.45.128 is the network address o The line is after 64, so add 64 to get the network address of the next subnet The next subnet begins at 198.22.45.192 o So the broadcast address is 198.22.45.191 o And the valid host addresses are 198.22.45.129 to 198.22.45.190 Public IP Address vs Private IP Address IP Address = A unique number that identifies every device on a network.Transport Layer Reliability o TCP/IP provides two transport layer protocols: o TCP provides reliable and ordered delivery o UDP does not guarantee delivery or order o TCP uses acknowledgments to confirm receipt o TCP retransmits lost data when needed (C) 2020 Cisco and/or its affiliates. o The UDP header is simpler than TCP because it only adds 4 fields and requires only 8 bytes (i.e., 64 bits) of overhead when encapsulating the application layer data.The computers on a network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams Network Components o A network can be as simple as a single cable connecting two computers or as complex as a collection of networks that span the globe.o There are four essential characteristics that network architects must address to meet user expectations: o Fault Tolerance o Scalability o Quality of Service (QoS) o Security Fault Tolerance o A fault-tolerant network allows for a quick recovery when a network failure occurs.o Administrators must also protect packets that transmit over the network and the information stored on network-attached devices o There are three primary requirements for network security are: o Confidentiality: Ensures that only the intended and authorized recipients can access and read data.www.su.edu.om 20L24AN Topologies Half- Duplex and Full-Duplex www.su.edu.om LAN Topologies Half- Duplex and Full-Duplex o Half-Duplex Communication o Both devices can transmit and receive on the media but cannot do so simultaneously.www.su.edu.om LAN Topologies Half and Full Duplex (Cont.) o Full-Duplex Communication o Both devices can transmit and receive on the media at the same time.o Routing - The network layer providesservicesto direct the packets to a destination host on another network o De-encapsulation - When the packet arrives at the network layer of the destination host, the packet is de-encapsulated by the network layer, and the appropriate service at the transport layer passes up the resulting Layer 4 PDU.www.su.edu.om IP Encapsulation o IP encapsulates the transport layer segment adding an IP header.Cisco Confidential TCP Communication Process Session Termination o To close a TCP connection, TCP uses a four-way handshake involving the Finish (FIN) and Acknowledgment (ACK) control flags.149 Week 13 Hypertext Transfer Protocol and Hypertext Markup Language o When a web address or uniform resource locator (URL) is typed into a web browser, the web browser establishes a connection to the web service running on the server, using the HTTP protocol.Dynamic Host Configuration Protocol o The Dynamic Host Configuration Protocol (DHCP) for IPv4 automates the assignment of IPv4 addresses, subnet masks, gateways, and other parameters.o Application layer is the window for users and application processes to access network resources and services Layer 6: Presentation Layer o This layer is concerned with the actual format that data is presented in, data representation or syntax o Ensures that data that is sent by one application can be successfully read by another application.o An Ethernet MAC address is a 48-bit address expressed using 12 hexadecimal digits www.su.edu.om Ethernet MAC Address o All MAC addresses must be unique to the Ethernet device or Ethernet interface.www.su.edu.om Message Delivery Options Unicast Message Multicast Message Broadcast Message One-to-many One-to-all One-to-one o Different MAC addresses are used for Layer 2 unicast, broadcast, and multicast communications.www.su.edu.om IPv4 Packet Header o An IPv4 packet header consists of fields containing important information about the packet.Cisco Confidential Multiple Separate Communications o The TCP and UDP transport layer protocols use port numbers to manage multiple, simultaneous conversations.o Other types of networks: o Metropolitan Area Network (MAN) o Wireless LAN (WLAN) o Storage Area Network (SAN) Local Area Network (LAN) o Three characteristics of LANs: o Spans a small geographic area such as a home, school, office building, or campus.Wide Area Network (WAN) o Three characteristics of WANs: o WANs interconnect LANs over wide geographical areas such as between cities, states, or countries.o Quality of Service (QoS) is a primary mechanism for managing congestion and ensuring reliable content delivery to all users.o Data - application layer PDU o Segment - Transport layer PDU o Packet - Network layer PDU o Frame - Data Link Layer PDU o Bits - Physical Layer PDU Protocol Data Units Data Encapsulation o The encapsulation process works from top to bottom: o Data is divided into segments.Cisco Confidential Ethernet MAC Address MAC Address and Hexadecimal o In networking, the decimal base ten number system and the binary base 2 number system represent IPv4 addresses.21 www.su.edu.om Ethernet MAC Address o The MAC address is used to identify the physical source and destination devices (NICs) on the local network segment.o When a vendor assigns a MAC address to a device or Ethernet interface, the vendor must do as follows: o Use its assigned OUI as the first 6 hexadecimal digits.o The IP header is examined by Layer 3 devices (i.e., routers and Layer 3 switches) as it travels across a network to its destination.o Notify other devices of errors and communication failures Network Media o Communication across a network is carried through a medium which allows a message to travel from source to destination.Scalability o A scalable network can be expanded quickly to support new connections without degrading the performance of services that existing users are accessing.o When attempts of simultaneous communications are across the network, the demand for network bandwidth can exceed its availability, creating network congestion.this allows for interoperability TCP/IP Model o TCP/IP was developed during the 1970s by the US Department of Defense's (DoD) Advanced Research Projects Agency (ARPA).o It is a protocol stack which consists of multiple protocols including TCP (Transmission Control Protocol) and IP (Internet Protocol).o Whereas the OSI Reference Model is conceptual, the TCP/IP stack is used to transfer data in production networks.Week 6 Purpose of the Data Link Layer Providing Access to Media Packets exchanged between nodes may experience numerous data link layers and media transitions.The features of an Ethernet broadcast are as follows: o It has a destination MAC address of FF-FF-FF-FF-FF-FF in hexadecimal (48 ones in binary).o Other network layer protocols include routing protocols such as Open Shortest Path First (OSPF) and messaging protocols such as Internet Control Message Protocol (ICMP).www.su.edu.om Characteristics of IP o IP was designed as a protocol with low overhead.www.su.edu.om Media Independent o IP is media-independent: the same IP packet can travel over copper, fiber, or wireless.(routed traffic) 192.168.10.15 / 255.255.255.0 www.su.edu.om Local Subnet or Routed Traffic o For a destination address to be in the same subnet, the network portion has to be exactly 192.168.10.o They would split their /8 address allocation into smaller subnets and allocate these to different offices and types of hosts o For example if they received 15.0.0.0/8, they could allocate the subnet 15.0.1.0/24 to sales computers in New York, 15.0.2.0/24 to accounting PCs and 15.0.9.0/24 to sales computers in Boston.200.15.10.249 to 200.15.10.254 (network .248, broadcast .255) Other Class C Subnet Masks o We can carry on moving the line back a place o /28 (or 255.255.255.240) = 16 networks of 14 hosts each o /27 (or 255.255.255.224) = 8 networks of 30 hosts each o /26 (or 255.255.255.192) = 4 networks of 62 hosts each o /25 (or 255.255.255.128) = 2 networks of 126 hosts each o /24 (or 255.255.255.0) = 1 network of 254 hosts Practice Question o What are the network address, broadcast address, and valid host addresses for the IP address 198.22.45.173/26?PRIVATE IP o Used inside a local network o Assigned by your Router o NOT visible on the Internet o Can be reused in any network o Example: 192.168.1.5 Computer Networks - Year 1 Week 10 (C) 2020 Cisco and/or its affiliates.Cisco Confidential Role of the Transport Layer o Application layer programs generate data that must be exchanged between source and destination hosts.o To support reliable communication, TCP adds a header with a minimum size of 20 bytes (160 bits) when encapsulating application data.o This header contains fields such as source port, destination port, sequence number, acknowledgment number, flags, window size, and checksum.Cisco Confidential TCP Communication Process TCP Connection Establishment o A client establishes a TCP connection with the server using the three-way handshake process.o Clients are computer hosts that have software installed enabling the hosts to request and display the information obtained from the server.o An example of client software is a web browser, such as Internet Explorer, Safari, Mozilla Firefox, or Chrome.o Wide Area Network (WAN) - spans a large geographic area typically involving a telecommunications service provider.o WANs are then connected to each other using copper wires, fiber optic cables, and wireless transmissions.o Split development (split areas of concern and application developer.) o We have seamless interoperability where traffic is same between multiple vendors and multiple applications.o Splits the message into smaller units if they are not small enough and then passes the smaller units down to the network layer for sending o It also handles transportation issues between hosts and ensures data transport reliability.Comparing the OSI Model with the TCP/IP Stack Data Encapsulation Protocol Data Units o As application data is passed down the protocol stack, information is added at each level.Some of the limitations of wireless: o Coverage area - Effective coverage can be significantly impacted by the physical characteristics of the deployment location.Many users accessing the WLAN simultaneously results in reduced bandwidth for each user.o Ethernet switches operate in full-duplex mode by default, but can operate in half-duplex if connecting to a device such as an Ethernet hub.2024 www.su.edu.om Ethernet MAC Address www.su.edu.om Ethernet MAC Address o For example, assume that Cisco needs to assign a unique MAC address to a new device.o These are the essential characteristics of IP: o Connectionless: There is no connection with the destination established before sending data packets.IP provides no capability for packet retransmissions if errors occur.o Layers 1-2 carry bits (electrical/light/radio), but IP (Layer 3) stays the same for addressing and routing.www.su.edu.om The Subnet Mask Network and Host Portion o An IPv4 address has two parts: Network portion + Host portion.Broadcast Address: 192.168.10.255 convert the both address to binary/ or only convert the host part to binary host host part (because in part we have 0, change all 0s in network part to 1s) 2025 www.su.edu.om From this given address 162.192.127.200 /16 find the following: 1.Broadcast Address Week 9 o The bigger the host portion of the network, the more hosts we can have o If the subnet mask is /8, we have 24 bits available to allocate to hosts o If the subnet mask is /24, we only have 8 bits available to allocate to hosts Class A o The internet authorities split the IPv4 address space into separate classes.o The default subnet mask is /8 o Valid network addresses range from 1.0.0.0 to 126.0.0.0 /8 o This allows for 126 networks and 16,777,214 hosts per network.o /31 subnets are supported on Cisco routers for point to point links (which have no need for a network or broadcast address.) Class C /30 Subnet o Let's move the line back a place.We're now using /29 (or 255.255.255.248) o This leaves 3 bits for the host address, 2 3 minus 2 = 6 possible hosts o It borrows 5 bits for the network address o This gives us 32 subnets (2 5 ) which accommodate 6 hosts each Class C /29 Subnet o Notice that the line is after the 8.Static addressing is used for network devices, such as gateways, switches, servers, and printers.o Network infrastructure contains three broad categories of network components: o Devices o Media o Services Network Components o End Devices o An end device is where a message originates from or where it is received.o Data originates with an end device, flows through the network, and arrives at an end device Intermediary Network Devices o An intermediary device interconnects end devices in a network.Cisco Confidential Peer-to-Peer Networks o Client and server software usually run on separate computers, but it is also possible for one computer to run both client and server software at the same time.o In larger businesses, because of the potential for high amounts of network traffic, it is often necessary to have dedicated servers to support the number of service requests.o Integrity: Assures users that the information does not alter in transmission from origin to destination.o Availability: Assures users of timely and reliable access to data services for authorized users.o It makes it easier for network engineers to discuss specific issues with devices such as routers or switches when host A sends traffic to host B. o Describes how does that communication actually take place between two devices in the network.o simplify teaching and learning as well as troubleshooting in the real world layer 7 Application layer o layer 7 Application layer o provides and network processes to applications.when using an MP3 you could connect to a Web site running an Apache server on Linux from your windows machine or from a mobile device such as an iPhone.Layer 2: Data Link Layer o Layer 2 or the data link layer o provides physical addressing and access to media o it is concerned with how data is formatted from upper layers for transmission over a given network technology.Layer1: Physical Layer o The first layer in the OSI Model or Layer1 is the Physical Layer o It defines how data is transmitted, so in other words, what states represents binary 1s or binary 0s.o TCP/IP is also layered but does not use all of the OSI layers, though the layers are equivalent in operation and function.o Security - Wireless communication coverage requires no access to a physical strand of media, so anyone can gain access to the transmission.At each hop along the path, a router performs four basic Layer 2 functions: o Accepts a frame from the network medium.A data link frame has three parts: o Header o Data o Trailer The fields of the header and trailer vary according to data link layer protocol.o Hexadecimal is used to identify an Ethernet address because a single hexadecimal digit represents four binary bits.MAC addressing provides a method for device identification at the data link layer of the OSI model.o Therefore, an Ethernet MAC address consists of a 6 hexadecimal vendor OUI code followed by a 6 o hexadecimal vendor-assigned value, as shown in the figure.o Routers implement routing protocols to route packets between networks.Cisco Confidential Connectionless o IP is connectionless, meaning that before data send, IP creates no dedicated end-to-end connection.Cisco Confidential Best Effort o IP is unreliable: it does not recover lost or corrupted packets.o If a router forwards to a smaller MTU, IPv4 may fragment the packet into smaller pieces.o Fragmentation adds overhead and can increase latency; losing one fragment can break the whole packet.o A subnet mask is 32 bits and can be written as dotted decimal (e.g., 255.255.255.0) or slash notation (e.g., /24).Subnet mask is in bits (/24), convert the bits to decimal format (remember in each octet only you can used 8 bits).o Rather than purchasing separate address ranges for the different departments, we can purchase a single range and subnet it into smaller portions.We're now using /30 (or 255.255.255.252) o This leaves 2 bits for the host address, 2 2 -2 = 2 possible hosts o It borrows 6 bits for the network address o This gives us 64 subnets (2 6 ) which accommodate 2 hosts each Class C /30 Subnet o Notice that the line is after the 4.PUBLIC IP o Used on the Internet o Assigned by your ISP o Visible to the whole world o Globally unique o Example: 41.44.100.5 VS ?Cisco Confidential User Datagram Protocol (UDP) o User Datagram Protocol (UDP): ?UDP Header o UDP is a stateless protocol, meaning neither the source or destination track the state of the communication session.o It uses the TCP SYN and ACK control bits (i.e., flags), and the sequence number field.o The DNS protocol defines an automated service that matches resource names with the required numeric network address.Domain Name Service o Domain names were created to convert the numeric IP addresses into a simple, recognizable name.o The DNS protocol defines an automated service that matches resource names with the required numeric network address.o Examples: o switches, wireless access points, routers, and firewalls.o The management of data as it flows through a network is also the role of an intermediary device including: o Regenerate and retransmit data signals.o Multiple PCs can also be connected to create a larger P2P network, but this requires a network device, such as a switch, to interconnect the computers.o WANs typically provide slower speed links between LANs.o It provides redundancy by using multiple paths between the source and destination.Week 3 OSI reference model o The OSI (Open Systems Interconnection) model is often used to explain communication between devices in a network.o allows for multi vendor interoperability and o rapid development.o Devices choose or select the best path to deliver data based on the information provided o OSPF or Open Shortest Path First.o BGP or border gateway protocol o ISIS or intermediate system to intermediate system.o The TCP segment is encapsulated in the IP Packet.Week 4 Physical Layer Characteristics Bandwidth o Bandwidth is the capacity at which a medium can carry data.o Digital bandwidth measures the amount of data that can flow from one place to another in a given amount of time; how many bits can be transmitted in a second.Limitations: o Attenuation - the longer the electrical signals have to travel, the weaker they get.Using the hexadecimal base sixteen number system represents IPv6 and Ethernet addresses.o The hexadecimal numbering system uses the numbers 0 to 9 and the letters A to F. o An Ethernet MAC address consists of a 48-bit binary value.Unicast MAC Address Broadcast MAC Address o An Ethernet broadcast frame is received and processed by every device on the Ethernet LAN.Cisco Confidential The MAC Address Table Switch Learning and Forwarding (Cont.) 34 (C) 2020 Cisco and/or its affiliates.o If the destination IPv4 address is on a different network than the source IPv4 address, the device will search the ARP table for the IPv4 address of the default gateway.o IP version 4 (IPv4) and version 6 (IPv6) are the principal network layer communication protocols.The destination host of the IP packet performs the de-encapsulation process.o The IP addressing information remains the same from when the packet leaves the source host until it arrives at the destination host.o Best Effort: IP is inherently unreliable because packet delivery is not guaranteed.o Connectionless communication is conceptually similar to sending a letter to someone without notifying the recipient in advance.7 Example: Voice Calls Over the Internet (VoIP, Zoom, WhatsApp Calls) oIf the internet connection is weak, you might hear gaps or missing wordsin a conversation.o Each link has an MTU (Maximum Transmission Unit): the largest packetsize allowed on that link.Differentiated Services or DiffServ (DS) - Used to determine the priority of each packet on the network.o If the destination is on a different subnet, the host sends traffic to the default gateway (router).Types ofAddresses in Network 192.168.10.0/24 o Network Address - host portion is all 0s (.00000000) o First Host address - host portion is all 0s and ends with a 1 (.00000001) o Last Host address - host portion is all 1s and ends with a 0 (.11111110) o BroadcastAddress - host portion is all 1s (.11111111) Calculate The Network, First Host, Last Host and Broadcast address From this given address 192.168.10.10/24 find the following: 1.Class B o Class B addresses are assigned to medium-sized to large-sized networks.o The default subnet mask is /16 o This allows for 16,384 networks and 65,534 hosts per network.o The default subnet mask is /24 o This allows for 2,097,152 networks and 254 hosts per network.o UDP achieves minimal overhead for each datagram.o The destination port number would be port 80 which informs the receiving server that web services are being requested.o HTTP Secure (HTTPS) protocol uses encryption and authentication to secure data.o Fully-qualified domain names (FQDNs), such as http://www.cisco.com, are much easier for people to remember than 198.133.219.25.o DHCP-distributed addresses are leased for a set period of time, then returned to pool for reuse.o The simplest P2P network consists of two directly connected computers using either a wired or wireless connection.o Provides high speed bandwidth to end and intermediary devices within the network.The Internet o The Internet is a worldwide collection of interconnected LANs and WANs.Network Characteristics o Networks support a wide range of applications and services over many different types of physical infrastructure.Quality of Service o Congestion occurs when the demand for network bandwidth exceeds the amount available.o provides access for users and application processes to utilize network services.o such as FTP telnet and HTTP are used at this layer.Layer 4: Transport Layer o Transport layer o Ensures end to end communication reliability and flow control.Layer 3: Network Layer o The network layer very important to us as a network engineers as this is where routers reside.o media signal and binary transmission are defined at this layer.o The IP packet is encapsulated in the Ethernet Frame.o De-encapsulation is the process used by a receiving device to remove one or more of the protocol headers.oIt is inexpensive, oeasy to install, and ohas low resistance to electrical current flow.Data Link Frame The Frame Data is encapsulated by the data link layer with a header and a trailer to form a frame.o Used in legacy bus topologies and with Ethernet hubs.o Data link layer assumes that the media is available for transmission for both nodes at any time.o The IEEE has assigned Cisco a OUI of 00-60-2F.Cisco would then configure the device with a unique vendor code such as 3A-07-BC.o It is flooded out all Ethernet switch ports except the incoming port.Cisco Confidential The MAC Address Table Switch Fundamentals (Cont.) The switch MAC address table is empty.o Media Independent: Operation is independent of the medium (i.e., copper, fiber?optic, or wireless) carrying the data.o If out-of-order packets are delivered, or packets are missing, then applications using the data, or upper-layer services, must resolve these issues.oThis happens because some packets carrying your voice did not reach the other person, and IP does not automatically resend them.Time-to-Live (TTL) - Limits the lifetime of a packet - decreased by one at each router along the way.o The host uses the subnet mask to determine the network portion and host portion of an IP address.o The subnet mask tells us where the split happens: o 1s = network bits o 0s = host bits o Example: IP = 192.168.10.15, Mask = 255.255.255.0 (/24) o Next step: write both in binary and use AND to find the network address.(local subnet) o If it wants to communicate with another host with any other network address(for example 192.168.11.20), it knows it has to send the traffic via a router.A logical AND is one of three basic binary operations used in digital logic.The Logical AND of two bits yields the following results: AND Network, Host, and Broadcast Addresses ?0 subnet mask after converting it from binary to decimal network part host part Continue 3.Now do Logical AND for ip address and subnet mask 192.168.10.10 00001010 255.255.255.0 00000000 192.168.10.0 00000000 network address AND Only convert the host part to binary number, then do the AND 2.o Class A addresses are assigned to networks with a very large number of hosts.o What is the subnet mask in dotted decimal notation?Practice Question Answer o Let's figure out the subnet mask in dotted decimal notation first because that's easy...o The transport layer is responsible for logical communications between applications running on different hosts.o Adding Header Information - The transport layer adds header information to identify the application and manage data delivery.UDP is a connectionless transport layer protocol ?TCP examples: web browsing, email, file transfer ?o The source port number is a unique, dynamically generated number that is associated with the originating application on the local host.o The destination port number is associated with the destination application on the remote host to identify the type of service being requested of the destination web server.o For example, when the host initiates the web page request: o The source port number is dynamically generated by the host to uniquely identify the conversation.o The handshake validates that the destination host is available to communicate.Host B acknowledges Host A (using ACK=101) and requests a session with Host A (using SEQ=300).o Therefore, a TCP conversation requires four exchanges to end both sessions.Email Protocols o Email clients communicate with mail servers to send and receive email.o Three protocols for email: o Simple Mail Transfer Protocol (SMTP) to send email.o Internet Message Access Protocol (IMAP) to retrieve email.SMTP Operation o SMTP is used to send email POP Operation o POP is used to retrieve email from a mail server.o Email is downloaded from the server to the client and then deleted on the server.o Copies of messages are downloaded from the server to the client and the original messages are stored on the server.Domain Name Service o Domain names convert the numeric address into a simple, recognizable name.o DHCP is usually employed for end user devices.o Each service requires separate server software.o For example, a host requires web server software in order to provide web services to the network.o Usually administered by multiple service providers.Network Security o Administrators must secure the physical network infrastructure and prevent unauthorized management access.The OSI model o The OSI model o provides a layered approach to development .o So to ensure that the receiving system can receive and understand the data, the data needs to be changed to machine independent format.You can listen to music view pictures watch videos and so forth because the data is presented in a format that both sides understand.o They use the logical addressing scheme of IP version 4 to determine the best path.o It is the main protocol stack used in computer operations today.o The form that the data takes at each layer is known as a Protocol Data Unit (PDU).o The data is de-encapsulated as it moves up the stack toward the end-user application.o Interference - Can be disrupted by many common devices.o Shared medium - WLANs operate in half-duplex, which means only one device can send or receive at a time.o De-encapsulates the frame to expose the encapsulated packet.o Forwards the new frame on the medium of the next network segment.Therefore, using only 12 hexadecimal values expresses a 48-bit Ethernet MAC address.o Assign a unique value in the last 6 hexadecimal digits.o A unicast MAC address is the unique address that is used when a frame is sent from a single transmitting device to a single destination device.o Delivering the packet to the destination host.o Packets may arrive corrupted, out of sequence, or may not arrive at all.Version - Specifies that the packet is IP version 4 ?o By comparing network portions, the host decides: local delivery or routing.Broadcast Address: to calculate the broadcast you need (network address and subnet mask), 11000000.10101000.00001010.00000000 Network address: 192.168.10.0 Subnet mask : 255.255.255.0 11111111 .111111111.Subnetting Class A o Obviously a company wouldn't put all 16,777,214 hosts into a single logical network, this would be terrible for performance and security.o This could be allocated as is for a real world network, or subnetted into smaller subnets.o It is the link between the application layer and the lower network transmission layers.o Datagram delivery is not guaranteed with UDP.Host A requests a TCP session with Host B (using SEQ=100)..Host B acknowledges Host A's FIN by sending an ACK.Host A acknowledges Host B's FIN by sending an ACK.HTTP and HTTPS o HTTP is a request/response protocol.o PUT - Uploads resources or content to the web server.o Mail servers communicate with other mail servers to transport messages from one domain to another.o Post Office Protocol (POP) to retrieve email.IMAP Operation o IMAP is used to retrieve mail from a mail server.o Maintain information about what pathways exist through the network and internetwork.(C) 2020 Cisco and/or its affiliates.o Small businesses and homes may operate a P2P network to share resources.8 (C) 2020 Cisco and/or its affiliates.o Usually administered by a single organization or individual.o LANs are connected to each other using WANs.o Linux Mac and Windows may format their data entirely differently.o An example is Ethernet which uses a MAC (Media Access Control) address as the identifier of a device.o Also called The TCP/IP Model or the Internet Model.This provides the greatest mobility option.o Re-encapsulates the packet into a new frame.The amount of control information carried with in the frame varies according to access control information and logical topology.o Contained in the frame header.o Updated by each device that forwards the frame.o WLANs also operate in half-duplex.(C) 2020 Cisco and/or its affiliates.o Therefore, the Ethernet MAC address of that device would be 00-60-2F-3A-07-BC.(C) 2020 Cisco and/or its affiliates.33 (C) 2020 Cisco and/or its affiliates.o Every IP device on an Ethernet network has a unique Ethernet MAC address.(C) 2020 Cisco and/or its affiliates.6 (C) 2020 Cisco and/or its affiliates.Source IPv4 Address - Source address of the packet.Destination IPv4 Address - Address of destination.o With /24, the first 3 octets are network, and the last octet is host.That would be a duplicate IP address.Used to determine the NetworkAddress ?Network Address 192.168.10.10/24 Ip address Subnet mask 1.To find the network address you need: (ip address and subnet mask) its given.Last Host Address: you can find the last host from the broadcast, so first calculate the broadcast.Last Host Address: 192.168.10.254
Computer Networks I
Week 1,2
Computer Networks
A computer network consists of two or more computing devices that are connected in order to
share the components of the network (its resources) and the information
A network consists of two or more computers that are linked in order to share resources (such
as printers), exchange files, or allow communications. The computers on a network may be
linked through cables, telephone lines, radio waves, satellites, or infrared light beams
Network Components
• A network can be as simple as
a single cable connecting two
computers or as complex as a
collection of networks that
span the globe.
• Network infrastructure
contains three broad
categories of network
components:
• Devices
• Media
• Services
Network Components
• End Devices
• An end device is where a message originates from or where it is received.
• Data originates with an end device, flows through the network, and arrives at
an end device
Intermediary Network Devices
• An intermediary device interconnects end devices in a network.
• Examples:
• switches, wireless access points, routers, and firewalls.
• The management of data as it flows through a network is also the role
of an intermediary device including:
• Regenerate and retransmit data signals.
• Maintain information about what pathways exist through the network and
internetwork.
• Notify other devices of errors and communication failures
Network Media
• Communication across a network is carried through a medium which
allows a message to travel from source to destination.
• Networks typically use three types of media:
• Metallic wires within cables, such as copper
• Glass, such as fiber optic cables
• Wireless transmission
Clients and Servers
• Servers are hosts that have software installed which enable them to
provide information, like email or web pages, to other hosts on the
network.
• Each service requires separate server software.
• For example, a host requires web server software in order to
provide web services to the network.
• Clients are computer hosts that have software installed enabling the
hosts to request and display the information obtained from the
server.
• An example of client software is a web browser, such as
Internet Explorer, Safari, Mozilla Firefox, or Chrome.
© 2020 Cisco and/or its affiliates. All rights reserved. Cisco Confidential
Peer-to-Peer Networks
• Client and server software usually run on separate computers, but it is also possible for one
computer to run both client and server software at the same time.
• This type of network is called a peer-to-peer (P2P) network.
• Small businesses and homes may operate a P2P network to share resources.
• The simplest P2P network consists of two directly connected computers using either a wired or
wireless connection.
• Both computers are then able to use this simple network to exchange data and services
with each other, acting as either a client or a server, as necessary.
• Multiple PCs can also be connected to create a larger P2P network, but this requires a network
device, such as a switch, to interconnect the computers.
• In larger businesses, because of the potential for high amounts of network traffic, it is often
necessary to have dedicated servers to support the number of service requests.
8
© 2020 Cisco and/or its affiliates. All rights reserved. Cisco Confidential
Peer-to-Peer Networks (Cont.)
Advantages of P2P networking:
• Easy to set up
• Less complex
• Lower cost because network devices and dedicated servers may not be required
• Can be used for simple tasks such as transferring files and sharing printers
Disadvantages of P2P networking:
• No centralized administration
• Not as secure
• Not scalable
• All devices may act as both clients and servers which can slow their performance
9
Network Types
• Two most common types of networks:
• Local Area Network (LAN) – spans a
small geographic area owned or
operated by an individual or IT
department.
• Wide Area Network (WAN) – spans a
large geographic area typically involving
a telecommunications service provider.
• Other types of networks:
• Metropolitan Area Network (MAN)
• Wireless LAN (WLAN)
• Storage Area Network (SAN)
Local Area Network (LAN)
• Three characteristics of LANs:
• Spans a small geographic area such as a home, school, office building, or campus.
• Usually administered by a single organization or individual.
• Provides high speed bandwidth to end and intermediary devices within the network.
Wide Area Network (WAN)
• Three characteristics of WANs:
• WANs interconnect LANs over wide geographical areas such as between cities, states, or
countries.
• Usually administered by multiple service providers.
• WANs typically provide slower speed links between LANs.
The Internet
• The Internet is a worldwide collection
of interconnected LANs and WANs.
• LANs are connected to each other
using WANs.
• WANs are then connected to each
other using copper wires, fiber optic
cables, and wireless transmissions.
Network Characteristics
• Networks support a wide range of applications
and services over many different types of
physical infrastructure.
• There are four essential characteristics that
network architects must address to meet user
expectations:
• Fault Tolerance
• Scalability
• Quality of Service (QoS)
• Security
Fault Tolerance
• A fault-tolerant network allows for a quick recovery when a network failure occurs.
• It provides redundancy by using multiple paths between the source and destination.
Scalability
• A scalable network can be expanded quickly to support new connections without degrading
the performance of services that existing users are accessing.
Quality of Service
• Congestion occurs when the demand for network bandwidth exceeds the amount available.
• When attempts of simultaneous communications are across the network, the demand for
network bandwidth can exceed its availability, creating network congestion.
• Quality of Service (QoS) is a primary mechanism
for managing congestion and ensuring reliable
content delivery to all users.
Network Security
• Administrators must secure the physical network infrastructure and prevent unauthorized
management access.
• Administrators must also protect packets that transmit over the network and the information stored
on network-attached devices
• There are three primary requirements for
network security are:
• Confidentiality: Ensures that only the
intended and authorized recipients can
access and read data.
• Integrity: Assures users that the
information does not alter in transmission
from origin to destination.
• Availability: Assures users of timely and
reliable access to data services for
authorized users.
Week 3
OSI reference model
• The OSI (Open Systems Interconnection) model is often used to explain communication
between devices in a network.
• It makes it easier for network engineers to discuss specific issues with devices such as
routers or switches when host A sends traffic to host B.
• Describes how does that communication actually take place between two devices in the
network.
The OSI model
• The OSI model
• provides a layered approach to development .
• allows for multi vendor interoperability and
• rapid development.
• Split development (split areas of concern and application
developer.)
• We have seamless interoperability where traffic is same
between multiple vendors and multiple applications.
• simplify teaching and learning as well as troubleshooting
in the real world
layer 7 Application layer
• layer 7 Application layer
• provides and network processes to applications.
• provides access for users and application processes to utilize network
services.
• such as FTP telnet and HTTP are used at this layer.
• Application layer is the window for users and application processes to
access network resources and services
Layer 6: Presentation Layer
• This layer is concerned with the actual format that data is presented in, data
representation or syntax
• Ensures that data that is sent by one application can be successfully read by another
application.
• Different systems have different ways of formatting their data.
• Linux Mac and Windows may format their data entirely differently.
• So to ensure that the receiving system can receive and understand the data, the data
needs to be changed to machine independent format.
when using an MP3 you could connect to a Web site running an Apache server on Linux from your
windows machine or from a mobile device such as an iPhone.
You can listen to music view pictures watch videos and so forth because the data is presented in a
format that both sides understand.
Layer 4: Transport Layer
• Transport layer
• Ensures end to end communication reliability and flow control.
• Splits the message into smaller units if they are not small enough and then passes
the smaller units down to the network layer for sending
• It also handles transportation issues between hosts and ensures data transport reliability.
Layer 3: Network Layer
• The network layer very important to us as a network engineers as this is where routers
reside.
• Devices choose or select the best path to deliver data based on the information provided
• OSPF or Open Shortest Path First.
• BGP or border gateway protocol
• ISIS or intermediate system to intermediate system.
• They use the logical addressing scheme of IP version 4 to determine the best path.
Layer 2: Data Link Layer
• Layer 2 or the data link layer
• provides physical addressing and access to media
• it is concerned with how data is formatted from upper layers for transmission over a given
network technology.
• It is also concerned with how access to the network is controlled.
• An example is Ethernet which uses a MAC (Media Access Control) address as the
identifier of a device.
Layer1: Physical Layer
• The first layer in the OSI Model or Layer1 is the Physical Layer
• It defines how data is transmitted, so in other words, what states represents
binary 1s or binary 0s.
• media signal and binary transmission are defined at this layer. this allows for
interoperability
TCP/IP Model
• TCP/IP was developed during the 1970s by the US Department of Defense’s (DoD)
Advanced Research Projects Agency (ARPA).
• It is a protocol stack which consists of multiple protocols including TCP (Transmission
Control Protocol) and IP (Internet Protocol).
• It is the main protocol stack used in computer operations today.
• Whereas the OSI Reference Model is conceptual, the TCP/IP stack is used to transfer data
in production networks.
• TCP/IP is also layered but does not use all of the OSI layers, though the layers are
equivalent in operation and function.
• Also called The TCP/IP Model or the Internet Model.
Comparing the OSI Model with the TCP/IP Stack
Data Encapsulation
Protocol Data Units
• As application data is passed down the
protocol stack, information is added at each
level. This is known as the encapsulation
process.
• The form that the data takes at each layer is
known as a Protocol Data Unit (PDU).
• Data - application layer PDU
• Segment – Transport layer PDU
• Packet – Network layer PDU
• Frame – Data Link Layer PDU
• Bits – Physical Layer PDU
Protocol Data Units
Data Encapsulation
• The encapsulation process works from top to
bottom:
• Data is divided into segments.
• The TCP segment is encapsulated in the IP
Packet.
• The IP packet is encapsulated in the
Ethernet Frame.
Data de-Encapsulation
• The de-encapsulation process works from
bottom to top.
• De-encapsulation is the process used by a
receiving device to remove one or more of the
protocol headers.
• The data is de-encapsulated as it moves up
the stack toward the end-user application.
Week 4
Physical Layer Characteristics
Bandwidth
• Bandwidth is the capacity at which a medium can carry data.
• Digital bandwidth measures the amount of data that can flow from one place to another in a
given amount of time; how many bits can be transmitted in a second.
Unit of Bandwidth Abbreviation Equivalence
Bits per second bps 1 bps = fundamental unit of bandwidth
Kilobits per second Kbps 1 Kbps = 1,000 bps = 103 bps
Megabits per second Mbps 1 Mbps = 1,000,000 bps = 106 bps
Gigabits per second Gbps 1 Gbps – 1,000,000,000 bps = 109 bps
Terabits per second Tbps 1 Tbps = 1,000,000,000,000 bps = 1012 bps
Physical Layer Characteristics
Bandwidth Terminology
Latency
• Amount of time, including delays, for data to travel from one given point to another
Throughput
• The measure of the transfer of bits across the media over a given period of time
Goodput
• The measure of usable data transferred over a given period of time
• Goodput = Throughput - traffic overhead
• Traffic Overhead: This is the extra data added to manage the transfer, such as packet
headers, error-checking bits, or control information
Copper Cabling
Characteristics of Copper Cabling
Copper cabling is the most common type of
cabling used in networks today.
•It is inexpensive,
•easy to install, and
•has low resistance to electrical current flow.
Limitations:
• Attenuation – the longer the electrical
signals have to travel, the weaker they
get.
Copper Cabling
Shielded Twisted Pair (STP)
• More expensive than UTP
• Harder to install than UTP
• Terminated with RJ-45 connectors
• Interconnects hosts with intermediary
network devices
Copper Cabling
Coaxial Cable
There are different types of connectors used with coax cable.
Commonly used in the following situations:
• Wireless installations - attach antennas to wireless devices
• Cable internet installations - customer premises wiring
Ethernet
Straight-through and Crossover UTP Cables
Connections of a Router for Ethernet
Straight through used to
connect:
• Switch-to-Router, Switchto-PC, Router-to-Server,
Hub-to-PC, Hub-to-Server
Cross-over used to
connect:
• Switch-to-Switch, PC-toPC, Switch-to-Hub, Hubto-Hub, Router-to-Router
Cisco Network Academy, https://www.netacad.com/courses/
Fiber-Optic Cabling
Properties of Fiber-Optic Cabling
• Not as common as UTP because of the expense involved
• Ideal for some networking scenarios
• Transmits data over longer distances at higher bandwidth than any other networking
media
• The fiber-optic cable acts as a wave guide to transmit light between the two ends with
minimal signal loss
Fiber-Optic Cabling
Fiber versus Copper
Implementation Issues UTP Cabling Fiber-Optic Cabling
Bandwidth supported 10 Mb/s - 10 Gb/s 10 Mb/s - 100 Gb/s
Distance Relatively short (1 - 100
meters)
Relatively long ( 1 - 100,000
meters)
Immunity to electrical
hazards Low High (Completely immune)
Media and connector
costs
Lowest Highest
Installation skills required Lowest Highest
Safety precautions Lowest Highest
Wireless Media
Properties of Wireless Media
It carries electromagnetic signals representing binary digits using radio or microwave
frequencies. This provides the greatest mobility option.
Some of the limitations of wireless:
• Coverage area - Effective coverage can be significantly impacted by the physical characteristics
of the deployment location.
• Interference - Can be disrupted by many common devices.
• Security - Wireless communication coverage requires no access to a physical strand of media,
so anyone can gain access to the transmission.
• Shared medium - WLANs operate in half-duplex, which means only one device can send or
receive at a time. Many users accessing the WLAN simultaneously results in reduced
bandwidth for each user.
Week 6
Purpose of the Data Link Layer
Providing Access to Media
Packets exchanged between nodes may experience numerous data link
layers and media transitions.
At each hop along the path, a router performs four basic Layer 2 functions:
• Accepts a frame from the network medium.
• De-encapsulates the frame to expose the
encapsulated packet.
• Re-encapsulates the packet into a new frame.
• Forwards the new frame on the medium of the
next network segment.
Data Link Frame
The Frame
Data is encapsulated by the data link layer with a header and a trailer to form a frame.
A data link frame has three parts:
• Header
• Data
• Trailer
The fields of the header and trailer vary according to data link layer protocol.
The amount of control information carried with in the frame varies according to access control
information and logical topology.
Data Link Frame
Frame Fields
Field Description
Frame Start and Stop Identifies beginning and end of frame
Addressing Indicatessource and destination nodes
Type Identifies encapsulated Layer 3 protocol
Control Identifies flow controlservices
Data Containsthe frame payload
Error Detection Used for determine transmission errors
Data Link Frame
Layer 2 Addresses
• Also referred to as a physical address.
• Contained in the frame header.
• Used only for local delivery of a frame on the link.
• Updated by each device that forwards the frame.
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20L24AN Topologies
Half- Duplex and Full-Duplex
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LAN Topologies
Half- Duplex and Full-Duplex
• Half-Duplex Communication
• Both devices can transmit and receive
on the media but cannot do so
simultaneously.
• Used in legacy bus topologies and with
Ethernet hubs.
• WLANs also operate in half-duplex.
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Half and Full Duplex (Cont.)
• Full-Duplex Communication
• Both devices can transmit and receive
on the media at the same time.
• Data link layer assumes that the media
is available for transmission for both
nodes at any time.
• Ethernet switches operate in full-duplex
mode by default, but can operate in
half-duplex if connecting to a device
such as an Ethernet hub.
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Ethernet MAC Address
MAC Address and Hexadecimal
• In networking, the decimal base ten number system and the binary base 2 number system
represent IPv4 addresses. Using the hexadecimal base sixteen number system represents IPv6
and Ethernet addresses.
• The hexadecimal numbering system uses the numbers 0 to 9 and the letters A to F.
• An Ethernet MAC address consists of a 48-bit binary value.
• Hexadecimal is used to identify an Ethernet address because a single hexadecimal digit
represents four binary bits. Therefore, using only 12 hexadecimal values expresses a 48-bit
Ethernet MAC address.
21
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Ethernet MAC Address
• The MAC address is used to identify the physical source and destination devices (NICs) on
the local network segment. MAC addressing provides a method for device identification at
the data link layer of the OSI model.
• An Ethernet MAC address is a 48-bit address expressed using 12 hexadecimal digits
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Ethernet MAC Address
• All MAC addresses must be unique to the Ethernet device or Ethernet
interface. To ensure this, all vendors that sell Ethernet devices must
register with the IEEE to obtain a unique 6 hexadecimal (i.e., 24-bit or
3-byte) code called the organizationally unique identifier (OUI).
• When a vendor assigns a MAC address to a device or Ethernet
interface, the vendor must do as follows:
• Use its assigned OUI as the first 6 hexadecimal digits.
• Assign a unique value in the last 6 hexadecimal digits.
• Therefore, an Ethernet MAC address consists of a 6 hexadecimal
vendor OUI code followed by a 6
• hexadecimal vendor-assigned value, as shown in the figure.
2024 www.su.edu.om Ethernet MAC
Address
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Ethernet MAC Address
• For example, assume that Cisco needs to assign a unique MAC
address to a new device.
• The IEEE has assigned Cisco a OUI of 00-60-2F. Cisco would then
configure the device with a unique vendor code such as 3A-07-BC.
• Therefore, the Ethernet MAC address of that device would be
00-60-2F-3A-07-BC.
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Message Delivery Options
Unicast Message Multicast Message Broadcast Message
One-to-many One-to-all One-to-one
• Different MAC addresses are used for Layer 2 unicast, broadcast, and multicast communications.
• A unicast MAC address is the unique address that is used when a frame is sent from a single
transmitting device to a single destination device.
Unicast MAC Address
Broadcast MAC Address
• An Ethernet broadcast frame is received and processed by every device on the Ethernet LAN. The
features of an Ethernet broadcast are as follows:
• It has a destination MAC address of
FF-FF-FF-FF-FF-FF in hexadecimal (48
ones in binary).
• It is flooded out all Ethernet switch ports
except the incoming port.
© 2020 Cisco and/or its affiliates. All rightsreserved. Cisco Confidential
The MAC Address Table
Switch Fundamentals (Cont.)
The switch MAC address table is empty.
33
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The MAC Address Table
Switch Learning and Forwarding (Cont.)
34
© 2020 Cisco and/or its affiliates. All rightsreserved. Cisco Confidential
The MAC Address Table
Filtering Frames (Cont.)
35
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IP to Mac Address resolution
• If your network uses the IPv4 communications protocol, you need ARP to map IPv4
addressesto MAC addresses.
• Every IP device on an Ethernet network has a unique Ethernet MAC address.
• ARP Address Resolution Protocol is used to map the IP address to MAC address
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• The sending device willsearch its ARP table for a destination IPv4 address and a
corresponding MAC address:
• If the packet’s destination IPv4 address is on the same network as the source IPv4
address, the device will search the ARP table for the destination IPv4 address.
• If the destination IPv4 address is on a different network than the source IPv4
address, the device will search the ARP table for the IPv4 address of the default
gateway.
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ARP Address Resolution Protocol
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ARP Address Resolution Protocol
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ARP Address Resolution Protocol
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ARP Address Resolution Protocol
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ARP Address Resolution Protocol
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Traffic
• When the sender and receiver are on different IP subnets, the traffic must be forwarded
by a router
• In the following example, 172.23.4.1/24 wants to send a packet to 192.168.10.1/24
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Traffic
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Traffic
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Traffic
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Traffic
www.su.edu.om Routed
Traffic
Week 7
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The Network Layer
• The network layer, or OSI Layer 3, provides
services to allow end devices to exchange
data across networks.
• IP version 4 (IPv4) and version 6 (IPv6) are
the principal network layer communication
protocols.
• Other network layer protocols include
routing protocols such as Open Shortest Path
First (OSPF) and messaging protocols such as
Internet Control Message Protocol (ICMP).
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The Network Layer
• Network layer protocols perform four basic operations :
• Addressing end devices - A unique IP address
• Encapsulation - The network layer encapsulates the protocol data unit (PDU) from the
transport layer into a packet.
• Routing - The network layer providesservicesto direct the packets to a destination host
on another network
• De-encapsulation - When the packet arrives at the network layer of the destination
host, the packet is de-encapsulated by the network layer, and the appropriate service at
the transport layer passes up the resulting Layer 4 PDU. The destination host of the IP
packet performs the de-encapsulation process.
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IP Encapsulation
• IP encapsulates the transport layer segment adding an IP header.
• Delivering the packet to the destination host.
• The IP header is examined by Layer 3 devices (i.e., routers and Layer 3 switches) as it
travels across a network to its destination.
• The IP addressing information remains the same from when the packet leaves the source
host until it arrives at the destination host.
• Routers implement routing protocols to route packets between networks.
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Characteristics of IP
• IP was designed as a protocol with low overhead.
• These are the essential characteristics of IP:
• Connectionless: There is no connection with the destination established before
sending data packets.
• Best Effort: IP is inherently unreliable because packet delivery is not guaranteed.
• Media Independent: Operation is independent of the medium (i.e., copper, fiberoptic, or wireless) carrying the data.
© 2020 Cisco and/or its affiliates. All rightsreserved. Cisco Confidential
Connectionless
• IP is connectionless, meaning that before data send, IP creates no dedicated end-to-end
connection.
• Connectionless communication is conceptually similar to sending a letter to someone without
notifying the recipient in advance.
6
© 2020 Cisco and/or its affiliates. All rightsreserved. Cisco Confidential
Best Effort
• IP is unreliable: it does not recover lost or
corrupted packets.
• Packets may arrive corrupted, out of sequence,
or may not arrive at all. IP provides no capability
for packet retransmissions if errors occur.
• If out-of-order packets are delivered, or packets
are missing, then applications using the data, or
upper-layer services, must resolve these
issues.
7
Example: Voice Calls Over the Internet (VoIP,
Zoom, WhatsApp Calls)
•If the internet connection is weak, you might
hear gaps or missing wordsin a conversation.
•This happens because some packets carrying
your voice did not reach the other person, and
IP does not automatically resend them.
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Media
Independent
• IP is media-independent: the same IP packet can travel over
copper, fiber, or wireless.
• Layers 1–2 carry bits (electrical/light/radio), but IP (Layer 3) stays
the same for addressing and routing.
• Each link has an MTU (Maximum Transmission Unit): the largest
packetsize allowed on that link.
• If a router forwards to a smaller MTU, IPv4 may fragment the
packet into smaller pieces.
• Fragmentation adds overhead and can increase latency; losing one
fragment can break the whole packet.
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IPv4 Packet Header
• An IPv4 packet header consists of fields containing important information about the
packet.
Version – Specifies that the packet is IP version 4
Differentiated Services or DiffServ (DS) – Used to
determine the priority of each packet on the network.
Time-to-Live (TTL) – Limits the lifetime of a packet –
decreased by one at each router along the way.
Protocol – Used to identify the next level protocol.
Source IPv4 Address – Source address of the packet.
Destination IPv4 Address – Address of destination.
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IP Addresses
• IPv4 address is expressed as a 32 binary bits and it is divided into Four
Octets, each has 8-bits
• For example 192.168.10.15
• Each octet is 8 bits long (4x8=32)
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IP Address Octets
• Each octet in the IP address has a value ranging from 0 to 255
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IP Address Octets
• 192.168.10.15 =11000000.10101000.00001010.00001111
1
192
168
10
15
2 3 4
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The Subnet Mask
• If the destination is on the same subnet, the host sends traffic directly (through switches).
• If the destination is on a different subnet, the host sends traffic to the default gateway (router).
• The host uses the subnet mask to determine the network portion and host portion of an IP
address.
• By comparing network portions, the host decides: local delivery or routing.
• A subnet mask is 32 bits and can be written as dotted decimal (e.g., 255.255.255.0) or slash
notation (e.g., /24).
www.su.edu.om The Subnet Mask
Network and Host
Portion
• An IPv4 address has two parts: Network portion + Host portion.
• The subnet mask tells us where the split happens:
• 1s = network bits
• 0s = host bits
• Example: IP = 192.168.10.15, Mask = 255.255.255.0 (/24)
• Next step: write both in binary and use AND to find the network address.
• With /24, the first 3 octets are network, and the last octet is host.
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Subnet
‘Masking’
• 192.168.10.15 / 255.255.255.0
• The IP address is compared (‘masked’) with the subnet mask
• A ‘1’ in the subnet mask indicates that bit in the IP address is part of
the network address
• A ‘0’ indicates the bit is part of the host address
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Subnet
‘Masking’
• 192.168.10.15 / 255.255.255.0
• The IP address is compared (‘masked’) with the subnet mask
• A ‘1’ in the subnet mask indicates that bit in the IP address is part of the network
address
• A ‘0’ indicates the bit is part of the host address
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The Network Portion
• 192.168.10.15 / 255.255.255.0
• In our example, the network address portion is 192.168.10
• The host address portion is .15
www.su.edu.om Local Subnet or Routed
Traffic
• If the host wants to communicate with another host with an IP address which also begins
with 192.168.10. (for example 192.168.10.20), it knows it’s on the same subnet and it
can send the traffic directly. (local subnet)
• If it wants to communicate with another host with any other network address(for
example 192.168.11.20), it knows it has to send the traffic via a router. (routed traffic)
192.168.10.15 / 255.255.255.0
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Traffic
• For a destination address to be in the same subnet, the network
portion has to be exactly 192.168.10.
• Otherwise it’s in a different subnet and traffic must be sent via a
router
192.168.10.15 / 255.255.255.0
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Valid Subnet Masks
• 192.168.10.15 / 255.255.255.0
• The subnet mask always begins with contiguous ‘1’s
• For example, 11111111.11110000.00000000.00000000 is a legal
subnet mask
• 11101101.11110000.11100000.00001111 is not
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Host Portion
• 192.168.10.15 / 255.255.255.0
• The host portion of the addressis available to be allocated to the different hosts on the
subnet (eg PCs, Servers, Printers, Router Interfaces and Switch Management Addresses)
• With two exceptions (coming up after the next slide)...
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Host Address
• The host portion of the address specifies the individual host and must be unique on that
subnet
• Hosts do not have to be numbered sequentially
• If the network portion of the address is 10.10.10, you can have a host with IP address
10.10.10.10 and another host with 10.10.10.20
• You can’t have two different hosts both with IP address 10.10.10.10. That would be a
duplicate IP address. Whenever another host sent traffic to 10.10.10.10, the network
wouldn’t know which one to send it to.
• We could have host 10.10.10.10 on one subnet and host 10.10.20.10 on another subnet
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The Network Address (Network ID)
• 192.168.10.15 / 255.255.255.0
• All 0’s in the host portion designates the network address and is not
allowed to be allocated to a host
• In our example the network address is 192.168.10.0
From Salih ALPEREN to Every
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The Broadcast Address
• 192.168.10.15 / 255.255.255.0
• All 1’s designates the directed broadcast address for the subnet
• Traffic with this destination address will be sent to all hosts in the
subnet
• In our example the broadcast address is 192.168.10.255
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Host Addresses
• That leaves 192.168.10.1 to 192.168.10.254 available to be allocated
to hosts
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Subnet Mask in Slash Notation
• 192.168.10.15 / 255.255.255.0
• Because the subnet mask always begins with contiguous ‘1’s, it will be
1 to 32 bits long counting from left to right
• This allows us to write the subnet mask in slash notation which is
more convenient than dotted decimal for network diagrams or in
conversation
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Subnet Mask in Slash Notation
• Our example can be written as either 192.168.10.15 255.255.255.0 or
192.168.10.15/24
• The network address is 192.168.10.0/24
• This example can be written as either 10.10.10.15 255.0.0.0 or
10.10.10.15/8
• The network address is 10.0.0.0/8
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Subnet Size
• The bigger the host portion of the network, the more hosts we can
have
• If the subnet mask is /8, we have 24 bits available to allocate to hosts
• If the subnet mask is /24, we only have 8 bits available to allocate to
hosts
Logical
AND
A logical AND is one of three basic binary
operations used in digital logic.
Used to determine the NetworkAddress
The Logical AND of two bits yields the
following results:
AND
Network, Host, and Broadcast
Addresses
Types ofAddresses in Network 192.168.10.0/24
• Network Address - host portion is all 0s (.00000000)
• First Host address - host portion is all 0s and ends with a 1
(.00000001)
• Last Host address - host portion is all 1s and ends with a 0
(.11111110)
• BroadcastAddress - host portion is all 1s (.11111111)
Calculate The Network, First Host, Last Host and Broadcast address
From this given address 192.168.10.10/24 find the following:
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